Hemlock. It is said that those who eat hemlock can see subjective things as objects. Thus, when Banquo had encountered the witches, who vanished as mysteriously as they appeared, he said to Macbeth, Were such things [really] here, . or have we eaten the insane root, that takes the reason prisoner, so that our eyes see things that are not. (Macbeth, i. 3.)

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Other plants take the reason prisoner, as the Pruna insana, the Indian nut, Hoary nightshade.